The retention of Cs+, Cd2+, Ph2+ and Cr3+ by the compounds formed as a result of the hydrothermal treatment of the bottom ash from the fluidized-bed incineration of municipal solid wastes is examined in this work. The amount of Cs+ retained and the distribution coefficient, K-d, were considerably lower than those for Cd2+, Ph2+ and Cr3+, independently of the type of compounds formed by the different bottom ash treatments. The high percentage of Cs+ retained (31%), with a K-d of 222 ml/g, occurred after treatment of the bottom ash in NaOH at 200 degrees C, where zeolite-type A (Na-6[AlSiO4]6 center dot 4H(2)O) was the major compound, together with aluminum tobermorite (Ca5Si5Al(OH)O-17-5H(2)O). In the case of Cd2+, Pb2+ and Cr3+, the amount retained was similar to 99% under all of the conditions studied. (c) 2005 Elsevier B.V. All rights reserved.